Arrangement and method for the analysis of the strength of a specimen of reducible material that contains iron

ABSTRACT

A method for the analysis of the strength of a test specimen (A) of reducible material that contains iron during the use of an arrangement that demonstrates a first device and a second device that can be displaced relative to each other, each of which demonstrates contact surfaces ( 8, 13 ) facing the other. The method comprises the steps: 
         a) a test specimen is arranged between the contact surfaces ( 8, 13 );    b) the distance between the contact surfaces ( 8, 13 ) is continuously reduced;    c) the test specimen (A) is compressed between the contact surfaces ( 8, 13 ) while a measurement value that comprises at least the force that is applied to the specimen (a) is collected; d) the measured value is stored in a memory; e) the distance between the contact surfaces is increased; and f) the compressed test specimen is removed. The invention further comprises an arrangement for carrying out the method.

The present invention concerns a method and an arrangement for the conduct of the method when analysing the strength of test specimens of reducible material that contain iron, as specified by the introduction to claim 1.

Extraction of metallic iron normally takes place through the reduction of iron oxide in a blast furnace or through its direct reduction in a direct reduction furnace. The iron oxide in the form of pellets comes into contact with a reducing gas, whereby the iron oxide is reduced to metallic iron in the form of molten iron, or what is known as sponge iron. The temperature of the reducing gas in the direct reduction process is approximately 800-950° C. If the pellets disintegrate during the reduction process, the contact of the reducing gas with the iron oxide is made more difficult, resulting in uneven operation and reduced productivity. For this reason, it is desired to obtain pellets of an even and high strength. The term “pellets” is here used to denote bodies composed of a reducible material containing iron that are in the form of agglomerates of finely divided material. Chemically pure iron ore concentrate that has been milled to a suitable size is mixed during the manufacture of pellets with an additive, and the mixture is then filtered to give a moist fibre cake. The moisture content of the fibre cake normally lies in the interval from 8 to 9% by weight. The moist filtered material is mixed with a binding agent and is rolled by known methods, for example, using rolling drums or rolling disks to give raw balls, known as green pellets, having a diameter of approximately 10-15 mm. The raw pellets are further processed by drying at an elevated temperature, in order subsequently to be sintered at high temperature to hardened pellets.

Moist raw pellets are weak and normally demonstrate a compressive strength of approximately 10 N/pellet. The low strength means that the pellets break easily. Broken pellets are separated out by sieving before the raw pellets are fed into the pelletizing machine, but raw pellets may break also after the sieving. The means that the penetrating ability of the gas in the bed of raw pellets during the process of forming pellets is reduced, and this in turn means that the drying, and the oxidation (if the iron ore concentrate is magnetite), cannot take place in an efficient and homogeneous manner. Furthermore, raw pellets are plastic, i.e. they can be deformed by pressure, and this further reduces the penetrability of the bed, since deformed pellets will close the spaces between that form between pellets that have a high strength, and through which spaces the gas is to pass.

When moist raw pellets are dried, binding agent and any other dissolved or finely divided material present collects at the points of contact between the particles that are components of the raw pellets. This creates new bonds, whereby a dry raw pellet demonstrates an increased strength when binding agent is used, typically in the interval 20-60 N/pellet.

If the iron ore concentrate is magnetite, the raw pellets are oxidised to hematite during the pelletization process. Further points of contact are formed between the particles that are components of the raw pellets, whereby the compressive strength typically amounts to approximately 500-800 N/pellet, although also other values may arise.

After the sintering, which normally takes place at approximately 1,300° C., the sintered pellet obtains a compressive strength greater than 2,000 N/pellet. It is important for several reasons to obtain a high and even strength of the pellets. In addition to the effects during the reduction process described above, also the strength during handling during transport is important. The final strength of the pellets is determined to a major extent by the strength of the raw pellets at the beginning of the pelletization process.

Different moisture contents, the fineness of the starting material, the amount of binding agent and the conditions during the mixing process are examples of parameters that give different strengths. A higher strength of the raw pellets and the pellets means that the pelletization process can be carried out at a higher capacity. Lower amounts of fines are created during the transport, and the productivity of the reduction process will be higher. The requirements for an even and high quality of the pellets is increasing, and this means that feedback between the quality of the pellets and the properties of the raw pellets is becoming ever more important. Random samples from the pellet production are taken in order to determine the strength of the final pellets used in the extraction of iron. The random samples are subjected to different types of test. Test methods for non-sintered pellets and for moist and dry raw pellets, however, have not been reliable, and there is for this reason a need for an efficient and reliable test method.

Arrangements for testing the hardness of test specimens are previously known. A common method of testing moist raw pellets is to drop the raw pellet a number of times from a pre-determined height. The number of times that the raw pellets can be dropped from that height without breaking gives the result of the test. The disadvantage of this method is that the result depends of the person conducting the test, i.e. the result can be unconsciously influenced by the person who carries out the test.

An arrangement for testing moist and dried raw pellets and pellets has been designed in such a manner that it can press the raw pellet or pellet to breakage through the application of a piston with increasing force until the raw pellet or pellet breaks. Reading takes place at the moment of breakage, either manually on a meter or automatically, as a maximum value before the diameter has been reduced by a certain percentage. The value of the force read is entered into a table. The disadvantage of this is that the applied force is not recorded during the complete pressure application process, and for this reason only information about the maximum force that was applied during the complete pressure application process can be obtained. It has proven to be the case that the maximum force can arise once the formation of cracks has begun in the raw pellet or pellets and thus in this manner give an erroneous image of the strength. Visual reading is imprecise and depends on the person who performs it. A further disadvantage of this arrangement is that it is designed in such a manner that the weak moist and dried raw pellets must be manually inserted one at a time.

If the moist, filtered material can be given an optimal moisture content, it demonstrates a sufficiently rapid growth during the rolling procedure, i.e. during the formation of raw pellets, maximal strength of the raw pellets formed, and sufficiently high plasticity such that it can survive the handling, and this is of major significance for the subsequent pelletization process.

One aim of the present invention is thus to provide an arrangement and a method for the analysis of properties of test specimens of reducible material that contains iron in its sintered or non-sintered form in the form of raw pellets and pellets, and to provide a subsequent report.

These aims are achieved through a method and an arrangement for the conduct of the method that demonstrates the characteristics and properties that are defined in the subsequent claims.

An embodiment selected as an example will be described below, with reference to the attached drawings, of which

FIG. 1 shows a press according to the invention, and

FIG. 2 shows the press from FIG. 1 with its cover removed.

The arrangement shown in FIG. 1 comprises a press 1 for test specimens A of reducible material that contains iron, in the form of green pellets, i.e. moist or dried raw pellets, or sintered pellets. The press 1 comprises a frame 2 with a base 3 in the form of a bottom part. A cover 4 is arranged over the frame 2 in the form of a pair of essentially vertical walls 5 at a distance from each other and a back piece 6. The cover 4 is provided with openings 7 for the connection of the press 1 with control and recording apparatus in the form of, for example, a computer, PLC or similar (not shown in the drawings).

A first device is arranged between the vertical walls 5, as is shown in FIG. 2, with a contact surface in the form of a pressure device 8 that can be displaced under control between a first withdrawn end position and a second extended position. The pressure device comprises, for example, a piston or a punch with a force that has been adapted for the current field of application. A force in the interval 0-100 N is used when testing raw pellets, while the measurement area is selected when testing sintered pellets such that the maximal force lies between 100-3,300 N. The speed of the pressure device 8 is set at between 2-50 mm/min in the preferred embodiment, and the distance of displacement of the pressure device 8 is set to 100 mm. The said speed and distance are regulated via an electric, hydraulic or pneumatic motor 9 and they are controlled by the said computer through a sensor.

A contact sensor 11 is arranged at the free end of the pressure device 8, at its surface 10 of contact, and it is intended that the contact sensor record the contact of the pressure device 8 with the surface of the pellet A. The pressure device may be driven with two or more different speeds in sequence, in order to minimise the time taken for pressure to be applied. The pressure device is fed forwards rapidly from its upper end position in a direction towards the test specimen. Rapid feed is ended before the contact sensor makes contact with the test specimen, at a distance from the end position that has been pre-determined. The contact sensor is used to measure the diameter of the test specimen, which diameter is read when the contact sensor makes contact with the test specimen. The cover 4 is furthermore provided with an opening 12 for access to a second device, arranged on the base 3, with a contact surface 13 in the form of an element having the shape of a platform, a disk, for example. This element can be rotated, preferably in the horizontal plane.

The disk 13 demonstrates on its surface 14 that faces the pressure device 8 a number of depressions or cavities 15, in which it is intended that test specimens A are placed in a manner that keeps them in place. The depressions 15 are symmetrically located at mutual distances from each other around the outer edge of the disk 13. The number of depressions 15 is 20 in this embodiment, but it must be realised that the number of depressions may be larger or smaller. The depressions 15 have a size that can accommodate a test specimen having a diameter in the interval 1-30 mm, a suggested interval is 5-15 mm. It is an advantage if the depressions have the form of bowls, whereby the test specimens can be displaced towards the centre of the depression in a simple manner during deployment. The disk in another embodiment has been designed with continuous walls or collars that surround the depressions. The task of the collars is to prevent dust and fragments from being spread inside the equipment when the test specimens are broken. The depressions in a further embodiment are only partially surrounded by collars in order to make possible an optical study of the breakage of the test specimens during the pressurisation procedure.

The disk 13 is arranged with a turning mechanism 16, such as a motor, a disc driven by a drive belt or a toothed wheel that is driven by a motor, and it may be disassembled to allow the depressions 15 of the disk 13 to be cleaned and to allow new test specimens to be placed into the depressions. The turning mechanism 16 is provided with an angle sensor in order to locate the depression of the disc at the correct location relative to the direction of motion of the pressure device 8.

Furthermore, a rotation coupling 17 is arranged between the turning mechanism 16 and the disk 13. The rotation coupling 17 is constructed with a loose structure or with play. The function of the looseness or play is to free the disk 13 from the turning mechanism 16 when the depression 15 of the disk is positioned in the correct manner, and in this way to free the mechanical contact between the disk 13 and the turning mechanism 16. This is necessary in order to avoid errors in the collection of data. The rotation of the disk 13 is coupled to the motion of the pressure device 8 in such a manner that when the pressure device 8 moves away from the disk 13, this disk is moved forward one step in order to position a new test specimen A in line with the direction of motion of the pressure device 8.

The contact surface 13 of the second device comprises in another embodiment an extended element with the form of a platform intended to receive a number of test specimens and to be moved forward, in its longitudinal direction, one step during the pressing operation.

It should be realised that both of the contact surfaces may in another embodiment be displaceable in a direction towards and away from each other, or that only the contact surface having the form of a platform may be displaceable in a direction towards the first contact surface.

At least one loading cell 18 is arranged in line with the pressure device 8 and the disk 13 that can be displaced in a direction along the direction of motion of the pressure device 8. The loading cell is selected in the same manner as the pressure device with respect to its field of operation. A loading cell with a measurement range in the interval, for example, 0-100 N is used when testing moist or dried raw pellets, while the measurement range is selected to lie between, for example, 0-1,000 N when testing partially hardened pellets. It should be realised that the measurement range of the loading cell is selected in order to correspond to the putative loading forces that can arise. The loading cell 18 is synchronised with the motions of the pressure device 8 and the disk 13, whereby the value of the load that is applied to the test specimen A is transferred to the computer.

The disk 13 is supported at three points distributed over the surface 14 of the disk that faces away from the pressure device 8, distributed as, for example, a triangle, in which one point comprises the loading cell 18 and the two other points comprise mechanical supports 19. The loading cell 18 is located in a line with the direction of motion of the pressure device 8 at the position at which the depressions 15 of the disk 13 are placed before each test. Loading cells 18 are arranged in another embodiment at two or at all of the support points. Sources of error during the collection of data are avoided if a loading cell is arranged at each support point, which error may arise if the test specimen is located obliquely in the depression, i.e. if the test specimen is not located centrally in the depression.

The loading cell 18 is in another embodiment arranged at the pressure device 8. The pressing procedure can in such an embodiment be the same as that described above, but it should be realised that the pressure device 8 may be arranged also as a fixed device whereby the surface of contact 13 is first moved forward one step in order to position a test specimen A at the correct position, after which the surface of contact 13 is displaced in a direction towards the pressure device 8 for the compression of the test specimen A.

The loading cell 18, the disk 13 and the pressure device 8 are, as has been described above, connected to a computer or to similar equipment. A test specimen is placed during testing in each depression after which the testing is sequentially carried out on all test specimens. The computer collects the measured values through the loading cell and the contact sensors of the pressure device, and stores these values in a storage medium in the form of a memory, for example a hard disk of the computer, in a manner that is previously known, after which a measurement file is generated. The measured values that are collected are, for example, sequence number of the test specimen A that is being tested, continuous measurement of the force that is applied by the pressure device 8 from the moment at which the pressure device makes contact with the test specimen until the test specimen disintegrates, i.e. until the pressure device has reached a specified reversal position, the magnitude of the distance between the pressure device 8 and the disk 13 when the pressure device makes contact with the test specimen, and the voltage across the contact sensor 11. It should be realised that also other values may be collected, depending of the aim and nature of the analysis. The rate at which the values are collected in this embodiment is 1,000 per second, but it may be 200,000 per second

The measured values that are collected are collated to a numerical report and to a graphical report. The underlying information for the numerical report is automatically created after each pressing operation. Examples of the values that are presented are diameter, force, classification as defined by the manner in which it disintegrates, deformation and any deviation from linearity.

The graphical report illustrates the force process during the pressure procedure and the crushing of each test specimen with respect to the motion of the pressure device. The collected values are plotted in a graph whereby, for example, the force is shown as a function of the time, from which the distance can be calculated, since the speed of the pressure device is known.

The present invention is not limited to what has been described above and shown in the drawings: it can be changed and modified in a number of different ways within the scope of the innovative concept specified by the attached claims. 

1. A method for the analysis of the strength of a test specimen of reducible material that contains iron during the use of an arrangement that demonstrates a first device and a second device that can be displaced relative to each other, each of which demonstrates contact surfaces facing the other, characterised by the steps: a) a test specimen is arranged between the contact surfaces; b) the distance between the contact surfaces is continuously reduced; c) the test specimen is compressed between the contact surfaces while a measurement value that comprises at least the force that is applied to the specimen is collected; d) the measured value is stored in a memory; e) the distance between the contact surfaces is increased; and f) the compressed test specimen is removed.
 2. The method according to claim 1, whereby a number of test specimens are brought between the contact surfaces after which the steps b-e are repeated in a sequence for each test specimen through one contact surface being displaced stepwise, after which step f) is carried out.
 3. The method according to claim 1, whereby the measured values are collected and processed by a computer, and are presented in a graphical report and a numerical report.
 4. The method according to claim 2, whereby the measured values are presented in real time during the measurement.
 5. An arrangement for the analysis of the strength of a test specimen intended to be used during the extraction of iron, comprising a frame on which a first device and a second device that are displaceable relative to each other, and that demonstrate contact surfaces that face each other, are arranged for the compression of a test specimen, characterised in that the contact surfaces comprise depressions for the reception of a test specimen and sensors for recording the measurement values that comprise at least the force that is applied to the specimen.
 6. The arrangement according to claim 5, whereby the second contact surface demonstrates a number of depressions.
 7. The arrangement according to claim 6, whereby the second contact surface is displaced in a stepwise manner for the sequential positioning of the depressions in line with the direction of motion of the first contact surface.
 8. The arrangement according to claim 6, whereby the second contact surface is rotated in a stepwise manner with the aid of a turning mechanism for the sequential positioning of the depressions in line with the direction of motion of the first contact surface.
 9. The arrangement according to claim 8, whereby the turning mechanism comprises a rotation coupling with which the second contact surface is released from mechanical contact with the turning mechanism during the compression.
 10. The arrangement according to claim 5, whereby the sensor comprises a loading cell for recording the measured values of the force that is applied to the test specimen from the contact surfaces during the compression.
 11. The arrangement according to claim 10, whereby the measured values that are collected comprise the diameter of the test specimen and the sequence number of the test specimen in a series of test specimens.
 12. The arrangement according to claim 10, whereby the value is stored in a memory unit that is connected to the contact surfaces.
 13. The arrangement according to claim 5, whereby the sensor is arranged in line with the direction of motion of the first contact surface.
 14. The arrangement according to claim 5, whereby the sensor is arranged at the first contact surface.
 15. The arrangement according to claim 5, whereby the first contact surface further comprises a contact sensor.
 16. The arrangement according to claim 5, whereby the device of the second contact surface comprises an element having the form of a platform.
 17. The arrangement according to claim 5, whereby the depressions comprise collars that fully or partially surround the depressions.
 18. The arrangement according to claim 5, whereby it comprises a cover with an opening provided with a hatch.
 19. The arrangement according to claim 18, whereby the opening is provided with a means of breaking the power supply to the first contact surface in the event that the hatch is opened during the compression. 